This disclosure is directed to a method of forming oxides of olefins, and particularly butylene and propylene oxides. The method of manufacture utilizes an electrolysis cell featuring a depolarized cathode for olefin oxide production.
This electrolytic process prepares butylene oxide or propylene oxide (BO or PO hereinafter). Electrolysis conversion of olefins to oxides is ordinarily handicapped by the production of hydrogen gas through HOH disassociation. Rather than use NaCl, the present process preferably uses KBr. An alternative salt is KCl. The process typically liberates elemental hydrogen. Because it is such a light weight molecule and diffuses readily, it is difficult to separate from the product and unreacted olefin. The hydrogen diffuses into the olefin oxide product and unreacted olefin removed from the electrolysis cell. After olefin oxide recovery, this then requires hydrogen separation so that the unreacted olefin can be recycled back to the cell. It is difficult to separate hydrogen and unreacted olefin to enable recycling of the olefin.
It has been discovered that the cathode is best a gas cathode. A continuous feed of oxygen to the cathode is highly desirable while a mixture of oxygen and nitrogen is also permissible. Cell voltage appears to be favorably reduced with pure oxygen in contrast with a nitrogen mix. As will be described, a mixture of the two can also be used to partially or significantly reduce electrode voltage. The gas supply to the cathode modifies the cathodic reaction. Ordinarily, the water solution adjacent the cathode decomposes into hydrogen and hydroxide ions. This leads to the production of hydrogen gas. However, furnishing oxygen in sufficient supply to the cathode enables the oxygen to react with the water, yielding only OH ions. No hydrogen gas is liberated.
The reactions occurring in the vicinity of the anode involves olefin conversion to form BO or PO. To the extent unreacted olefin is present, it can be readily separated from the olefin oxide produced without the added difficulty of separation from hydrogen. This enables the electrolyte, a metal halide (preferably an alkaline metal such as potassium) to be recycled repetitively. The electrolyte is then recycled to dissolve additional olefin to be processed, making the desired BO or PO. The absence of hydrogen from the electrolyte thus avoids difficult and expensive downstream separation process steps which could otherwise make the process unacceptable in commercial applications.
In summary, the process of this disclosure forms BO or PO and may be described as an olefin oxidation process which enables recycling of the supplied olefin until it is converted. This recycling enables the provision of economical and highly efficient process. This enables production of BO or PO in commercial quantities.